Etc on-board electronic tag and communication method

Abstract

The application relates to the technical field of traffic electronic toll collection, and discloses an ETC (Electronic Toll Collection) vehicle-mounted electronic tag and a communication method, wherein a communication security verification method comprises the following steps: extracting session parameters and generating a transition path seed; generating a transition token carrying timing information and sending a response message; acquiring a multi-antenna synchronous baseband signal and vehicle type medium parameters; calculating a net phase difference value after medium compensation; generating a phase feature digest value; embedding the phase feature digest value into a group cipher operation to generate an expected transition token fusing physical layer space information; and performing token comparison and aging verification and determining transaction legality.

Description

Technical Field

[0001] This invention relates to the field of electronic toll collection technology, specifically to an ETC (Electronic Toll Collection) vehicle-mounted electronic tag and communication method. Background Technology

[0002] In the ETC free-flow toll system, the on-board electronic tag completes transactions with the roadside unit of the gantry via the DSRC communication protocol. The roadside unit calculates the signal angle of arrival by using the phase difference of multiple antenna carriers to determine lane ownership and confirms the legality of the transaction by verifying the transition token in the response message.

[0003] In the existing system, physical layer lane location and application layer token verification operate independently. The physical layer relies solely on the angle of arrival (Angle of Arrival) to determine lane ownership, while the application layer relies solely on a time-lapse window to verify token validity. An attacker can deploy a replay device in an adjacent lane, using a directional antenna to simulate the signal incident angle of a target vehicle to deceive the Angle of Arrival location. Simultaneously, within the validity period of the lapse window, the attacker can rapidly replay the intercepted tag response message to pass validity verification. Because the two verification layers are independent, attackers can target both the physical and application layers separately, allowing cross-lane replay attacks to succeed even when both layers of verification pass independently, threatening ETC transaction security. Summary of the Invention

[0004] This invention provides an ETC (Electronic Toll Collection) vehicle-mounted electronic tag and communication method, which solves the technical problems in related technologies, such as the risk of replay attacks in the ETC communication process, the lack of effective physical channel feature binding verification methods, and the inaccurate determination of transaction legitimacy caused by cross-lane signal confusion.

[0005] This invention discloses an ETC vehicle-mounted electronic tag and communication method, which includes at least: the vehicle-mounted electronic tag extracts a session random number and a current timestamp from the activation command of the roadside unit, and concatenates the session random number with the current value of the monotonically increasing counter inside the tag to generate a transition path seed; When a state transition is triggered, the state code, the transition path seed, and the timing offset are input into the block cipher arithmetic unit to generate a transition token. The transition token and the attenuation window value are then embedded into the response message and sent to the roadside unit. The roadside unit performs baseband processing on the response signals received by multiple antennas to obtain a synchronous baseband signal, and performs medium compensation on the phase difference between adjacent antennas in combination with vehicle model medium parameters to obtain a net phase difference value. The net phase difference value is then hash-compressed to generate a phase feature summary value. The phase feature digest value and the session timing parameters are input into the block cipher arithmetic unit to generate the expected transition token. The received transition token is compared with the expected transition token, and the time difference is verified to see if it is within the effective range of the decay window, thereby determining the legality of the transaction.

[0006] Furthermore, the decay window value is generated based on the state transition timing decay function, which takes the timing offset as the independent variable and outputs a decay window value that decreases monotonically with the timing offset. The time offset is the time difference between the current time and the time reference point determined by the current timestamp, which is obtained by quantization with a preset precision.

[0007] Furthermore, the step of using vehicle model medium parameters to perform medium compensation for the phase difference between adjacent antennas to obtain the net phase difference value includes: Parse the vehicle type identification code from the response frame header, and retrieve the windshield nominal tilt angle, glass thickness and dielectric constant parameter group from the vehicle medium parameter table based on the vehicle type identification code; Based on the geometric installation position of the gantry antenna array and the estimated direction of arrival of the tag, calculate the geometric elevation angle between each antenna and the tag; For each antenna, the corresponding geometric elevation angle is taken as the incident angle, and the nominal tilt angle, glass thickness and dielectric constant parameter set are taken as the medium parameters. The plane wave oblique incidence multilayer medium transmission model is input to calculate the additional transmission phase value when the signal penetrates the windshield and generate the medium additional phase vector. The original phase difference value is extracted by performing conjugate multiplication on adjacent antennas in the synchronous baseband signal. The corresponding medium-added phase difference component is then subtracted from each original phase difference value to obtain the medium-compensated net phase difference value.

[0008] Furthermore, the plane wave oblique incidence multilayer dielectric transmission model treats the windshield as a planar dielectric layer with a uniform dielectric constant, specifically for the first... For an antenna, the incident angle of the signal relative to the glass normal is determined based on the geometric elevation angle and the nominal tilt angle. Then, the refraction angle of the signal inside the glass is calculated based on Snell's law. Based on the refraction angle and the glass thickness, the propagation path length of the signal along the refraction direction within the glass layer is determined. The additional transmission phase value corresponding to the antenna is calculated by combining the free space wavenumber and the square root of the dielectric constant.

[0009] Furthermore, subtracting the corresponding medium-added phase difference component from each original phase difference value includes: The first Subtract the first phase difference in the dielectric-added phase vector from the original phase difference between adjacent antennas. The component and the first The difference of the nth component is used to obtain the nth component. The net phase difference after media compensation, among which The range of values ​​is to , This represents the total number of roadside antennas.

[0010] Furthermore, the step of performing hash compression on the net phase difference to generate a phase feature digest value includes: A stable net phase difference vector is obtained by applying a sliding window mean filter to the sequence of net phase difference values. After performing fractional scaling normalization on each component of the stable net phase difference vector, a hash compression operation is performed to generate a fixed-length phase feature summary value.

[0011] Furthermore, the determination of the legality of the transaction based on this includes: If the tokens match and the time difference is within the effective range of the decay window, the response is deemed valid. The lane ownership result determined based on the stable net phase difference vector is then bound to the vehicle electronic tag identity information, and the transaction is advanced to the next state. If token matching fails or the time difference exceeds the decay window, the response is considered abnormal.

[0012] Furthermore, when determining an abnormal response, the following also applies: The vector distance between the net phase difference vector of the current abnormal response and the net phase difference vector of the historical passage tag of the adjacent lane is calculated to generate a cross-lane replay suspicion score. If the cross-lane replay suspicion score exceeds the preset threshold, the corresponding tag, abnormal message characteristics and phase difference vector deviation information will be reported to the background risk control system, and the abnormal marker will be broadcast to the adjacent vehicle roadside unit.

[0013] Furthermore, the vector distance calculation adopts the Euclidean distance algorithm, using the net phase difference vector of the current abnormal response as the query vector and the net phase difference vector of each legal passage tag recorded in the adjacent lane within a preset time range as the reference vector, and taking the minimum value among all Euclidean distances as the similarity measure; the cross-lane replay suspicion score is the reciprocal of the sum of the minimum value and a constant, and the smaller the minimum value, the higher the cross-lane replay suspicion score.

[0014] This invention provides an ETC (Electronic Toll Collection) vehicle-mounted electronic tag and communication system, comprising: The session parameter extraction and seed generation module is used to extract the session random number and the current timestamp from the activation command of the roadside unit, and to concatenate the session random number with the current value of the monotonically increasing counter inside the tag to generate the jump path seed. The token generation and response sending module is used to input the state code, the transition path seed and the timing offset into the block cipher operation unit to generate a transition token when the state transition is triggered, and to embed the transition token and the attenuation window value into the response message and send it to the roadside unit. The signal processing and medium compensation module is used to perform baseband processing on the response signals received by multiple antennas to obtain a synchronous baseband signal, and to perform medium compensation on the phase difference between adjacent antennas in combination with the vehicle model medium parameters to obtain a net phase difference value. A phase feature summary generation module is used to perform hash compression on the net phase difference to generate a phase feature summary value; The expected token generation module is used to input the phase feature digest value and the session timing parameters into the block cipher arithmetic unit to generate the expected transition token. The transaction validity determination module is used to compare the received transition token with the expected transition token and verify whether the time difference is within the effective range of the decay window, thereby determining the validity of the transaction.

[0015] This invention compensates for the phase difference of the tag's uplink signal based on vehicle model media parameters, eliminating the additional phase offset introduced by the windshields of different vehicle models, ensuring that the net phase difference reflects the tag's true spatial location information. After filtering and hash compression of the net phase difference, a phase feature digest value is generated, which encodes the combined features of the tag's physical location and the vehicle model media. This phase feature digest value is embedded in the block cipher process to generate the desired transition token, making the token verification result dependent on both the temporal offset and the physical layer spatial location information, thus achieving cross-binding between physical layer lane positioning and application layer anti-replay verification. When the physical location of the replay device differs from the original tag, the phase feature digest value calculated by the roadside unit changes, causing token comparison to fail. Attackers, without the block cipher key, cannot embed a forged phase feature digest value into the transition token, preventing them from breaking through both layers of verification separately, thus solving the security problem of the two layers of verification being attacked one by one when operating independently. Attached Figure Description

[0016] Figure 1 This is a flowchart of the ETC vehicle-mounted electronic tag and communication method provided in the embodiments of the present invention; Figure 2 This is a schematic diagram comparing the net phase difference vector between a legitimate passage and a replay attack scenario provided in an embodiment of the present invention; Figure 3 This is a schematic diagram showing the relationship between the geometric elevation angle and the incident angle of each antenna provided in the embodiments of the present invention; Figure 4 This is a schematic diagram of the additional phase values ​​of each antenna medium provided in the embodiments of the present invention; Figure 5 This is a schematic diagram comparing the phase difference vector filtering before and after according to an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating the change of the timing decay window value with time difference provided in an embodiment of the present invention; Figure 7This is a schematic diagram showing the comparison between cross-lane replay suspicion score and threshold provided in an embodiment of the present invention; Figure 8 This is a schematic diagram comparing the normalized phase feature vectors of legitimate passage and replay attacks provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of the timing offsets at each stage of the replay attack detection process provided in the embodiments of the present invention. Detailed Implementation

[0017] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0018] Example According to an embodiment of the present invention, an ETC (Electronic Toll Collection) vehicle-mounted electronic tag and communication method are as follows: Figure 1 As shown, it includes the following steps: Step 1: Extract session parameters and generate jump path seeds; The roadside unit sends an activation command to the vehicle-mounted electronic tag. The vehicle-mounted electronic tag extracts the session random number and the current timestamp from the activation command. The current timestamp is recorded as the timing reference point for this session. The session random number is concatenated with the current value of the tag's internal monotonically increasing counter to generate a transition path seed.

[0019] It should be noted that the above concatenation involves linking the binary sequence of the session's random number with the binary sequence of the current counter value in a predetermined order to form a fixed-length transition path seed. This transition path seed participates in token generation during subsequent cryptographic operations, ensuring the uniqueness of the token calculation path for each session. The counter is a monotonically increasing integer value maintained internally by the tag, incrementing once for each state transition to prevent token duplication within the same session.

[0020] Step 2: Generate a transition token carrying timing information and send a response message; When a tag state transition is triggered, the time difference between the current moment and the timing reference point is calculated, and the time difference is quantized into a timing offset with a preset precision. The current state code, the target state code, the transition path seed, and the timing offset are input together into a lightweight block cipher unit to generate a transition token carrying timing information.

[0021] The effective attenuation window value of the current transition token is calculated based on a preset state transition timing attenuation function. The transition token and attenuation window value are encoded and embedded in the extended field of the response message. The counter value is incremented and the transition path seed is updated. The response message is sent to the roadside unit via the tag antenna.

[0022] It should be noted that the preset precision of the aforementioned timing offset is a quantization granularity at the millisecond or microsecond level, and the specific precision is determined based on the DSRC communication frame interval. The aforementioned state transition timing decay function is based on the timing offset. As the independent variable, output the decay window value. Its expression is:

[0023] in, The initial attenuation window reference value, and They have the same time dimension; This is the decay rate coefficient, whose dimension is the reciprocal of time, and... The time units are reciprocals of each other, making the exponent term... It is a dimensionless quantity; This represents the timing offset between the current time and the timing reference point. It is a natural constant. Follow The monotonically decreasing nature of the transition token shortens its validity period as the transition time moves further away from the timeline reference point. The aforementioned lightweight block cipher unit performs symmetric cryptographic operations using a pre-shared key between the tag and roadside unit sides, employing the same algorithm and key on both sides.

[0024] Step 3: Obtain the multi-antenna synchronous baseband signal and vehicle model medium parameters; Get on the gantry The raw IQ data of the uplink response signal from the vehicle-mounted electronic tag received by the roadside antenna, among which This represents the total number of roadside antennas. Carrier synchronization and symbol timing recovery are performed on the IQ data of each antenna to generate... The road synchronization baseband signal is used. The vehicle type identification code is parsed from the response frame header. Based on the vehicle type identification code, the nominal tilt angle, glass thickness, and dielectric constant parameter groups of the windshield are retrieved from the vehicle medium parameter table.

[0025] It should be noted that the aforementioned vehicle model media parameter table is pre-stored in the local storage of the roadside unit, recording the mapping relationship between each vehicle model category identification code and the corresponding windshield physical parameters. The nominal tilt angle is the angle between the windshield plane and the horizontal plane. The glass thickness is the actual thickness of the windshield along the normal direction. The dielectric constant is the relative dielectric constant of the glass material at the DSRC operating frequency. The aforementioned carrier synchronization and symbol timing recovery are conventional baseband processing operations in the DSRC receive link, with the input being the original IQ sampling sequences of each antenna and the output being a time-aligned sequence. Synchronous baseband signal.

[0026] Step 4: Calculate the net phase difference after media compensation; Using a plane wave oblique incidence multilayer medium transmission model, targeting The geometric elevation angles between each antenna and the tag are used to calculate the additional transmission phase value when the signal penetrates the windshield, and generate... An additional phase vector is added to the medium. For In the synchronous baseband signal, adjacent antennas undergo conjugate multiplication to extract the original phase difference value. The corresponding dielectric-added phase difference component is then subtracted from each original phase difference value to obtain the... The net phase difference after medium compensation.

[0027] Step 4 may specifically include: Step 401: Based on the geometric installation position of the gantry antenna array and the estimated direction of arrival of the tag, calculate... The geometric elevation angle between each antenna and the tag.

[0028] Step 402: For each antenna, take the geometric elevation angle corresponding to the antenna as the incident angle, and take the nominal tilt angle, glass thickness and dielectric constant parameter set as the medium parameters. Input the plane wave oblique incident multilayer medium transmission model to calculate the additional transmission phase value when the signal penetrates the windshield.

[0029] It should be noted that the above plane wave oblique incidence multilayer dielectric transmission model assumes that the windshield has a uniform dielectric constant. The planar dielectric layer. For the first The antenna has a geometric elevation angle of 1 / 2 that is perpendicular to the tag. The angle of incidence of the signal in the air relative to the normal direction of the glass is ,in The nominal tilt angle of the windshield. This is the antenna serial number, with a value range of [value range missing]. to According to Snell's law, the angle of refraction of the signal inside the glass... satisfy The signal is at a thickness of The path length propagating along the refraction direction within the glass layer is The corresponding additional transmission phase value for:

[0030] in, The free-space wavelength corresponding to the DSRC operating frequency. For glass thickness, The relative permittivity of glass, For the first The angle of refraction of the signal corresponding to the antenna inside the glass. In the formula... is the free space wavenumber, with the dimension being the reciprocal of length; The refractive index is dimensionless. The length of the signal propagation path within the glass, with dimensions of length; the product of the three. The dimension of is dimensionless radians, which is consistent with the dimension of the original phase difference, so subtraction can be performed directly.

[0031] Step 403, will The arrangement of additional transmission phase values ​​corresponding to the root antennas An additional phase vector in a dimensional medium.

[0032] Step 404, for The first synchronous baseband signal in the circuit root antenna and the first Perform conjugate multiplication on the baseband signal of the root antenna to extract the first... For the original phase difference between adjacent antennas, where The range of values ​​is to .

[0033] Step 405, will the first Subtract the original phase difference value of adjacent antennas The third phase vector in the medium The component and the first The difference of the nth component is used to obtain the nth component. The net phase difference after medium compensation.

[0034] because Since the geometric elevation angles between the antennas and the tag are different, the additional transmission phase values ​​experienced by the signals received by each antenna are also different. By removing the additional phase difference component introduced by the medium from the original phase difference, the obtained net phase difference value can reflect the true spatial angle information of the tag, eliminating phase offset interference caused by vehicle model differences.

[0035] Step 5: Generate phase feature summary values; right A sliding window mean filter is applied to the sequence of net phase difference values ​​to obtain a stable net phase difference vector. After fractional scaling normalization of each component of the stable net phase difference vector, a hash compression operation is performed to generate a fixed-length phase feature summary value.

[0036] It should be noted that the aforementioned sliding window mean filtering averages the net phase difference sequence over a preset window length to suppress instantaneous phase jitter caused by multipath effects and thermal noise. Fractional scaling normalization maps each component of the stable net phase difference vector to a dimensionless numerical range, eliminating the influence of absolute phase value differences on the hash input and ensuring that the phase feature summary value only encodes the relative distribution characteristics between the components. The input to the hash compression operation is the normalized component values, and the output is a fixed-length binary summary value. Since different physical locations correspond to different antenna array angles of arrival, and different vehicle models produce different compensation amounts, the medium-compensated net phase difference vector is discriminative of the combination of the tag's spatial location and the vehicle model's medium, forming a compact feature representation after hash compression.

[0037] Step 6: Generate the desired transition token that integrates physical layer spatial information; The transition token and attenuation window value are extracted from the response message. The phase feature digest value, the time difference corresponding to the session timing reference point recorded by the roadside unit, the expected value of the local cached counter, and the session random number are input into the block cipher unit to generate the expected transition token that integrates physical layer spatial information.

[0038] It should be noted that the aforementioned block cipher unit uses the same cryptographic algorithm and key as the lightweight block cipher unit on the tag side in step 2. The roadside unit uses the phase digest value as one of the input parameters for cryptographic operations, making the value of the expected transition token, which incorporates physical layer spatial information, dependent on both the timing offset and the physical layer spatial location information. In a legitimate transaction scenario, the tag is in the correct physical location, and the phase digest value calculated by the roadside unit based on the actual received signal is consistent with the physical environment when the tag sends its response. Therefore, the expected transition token, which incorporates physical layer spatial information, matches the received transition token. In a replay attack scenario, the replay device is in a different physical location, and the phase digest value calculated by the roadside unit changes, causing the expected transition token, which incorporates physical layer spatial information, to mismatch with the intercepted original transition token.

[0039] Step 7: Perform token comparison and validity verification to determine the legality of the transaction; The received transition token is compared with the expected transition token that incorporates the physical layer spatial information. Simultaneously, it verifies whether the time difference falls within the effective range of the decay window. If the tokens match and the time difference is valid, the response is deemed valid, the lane affiliation result is bound to the vehicle's electronic tag identity information, and the transaction is advanced to the next state. If the token comparison fails or the time difference exceeds the decay window, the response is deemed abnormal.

[0040] It should be noted that the token comparison described above involves comparing the received transition token bit by bit with the expected transition token fused with the physical layer spatial information to ensure complete consistency. The timeliness verification described above determines whether the time difference between the moment the roadside unit receives the response message and the session timing reference point falls within the attenuation window value. Within the defined effective interval, i.e., to determine the time difference value of the roadside unit side. Does it meet the requirements? ,in The attenuation window value calculated in step 2, This is the time difference between the moment the roadside unit receives the response message and the session timing reference point. and Having the same time dimension, they can be directly compared. Both verification conditions must be met simultaneously; failure to meet either condition results in an abnormal response. When a response is deemed valid, the lane assignment result determines the tag's lane based on the estimated angle of arrival corresponding to the stable net phase difference vector, and the lane assignment result is associated with the tag's identity information and written into the transaction record.

[0041] In this embodiment of the application, in order to further identify cross-lane replay attack behavior and provide abnormal source tracing information to the back-end risk control system, based on the determination of abnormal response in step 7, the following steps are also included: Step 8: Generate a cross-lane replay suspicion score and report the abnormal information; If token matching fails, the net phase difference vector is compared with the net phase difference vector of the historical passage tags in the adjacent lanes to calculate the vector distance and generate a cross-lane replay suspicion score. If the cross-lane replay suspicion score exceeds a preset threshold, the corresponding tag identifier, abnormal message characteristics, and phase difference vector deviation information are reported to the backend risk control system. At the same time, an abnormal marker is broadcast to the adjacent lane-side units.

[0042] It should be noted that the above vector distance calculation uses the Euclidean distance algorithm. The net phase difference vector of the current abnormal response is used as the query vector, and the net phase difference vectors of each valid passage tag recorded by adjacent lanes within a preset time range are used as reference vectors. The Euclidean distance between the query vector and each reference vector is calculated one by one. Both the query vector and each reference vector are... The net phase difference vector has the same dimension, allowing direct Euclidean distance calculations. The minimum value among all Euclidean distances is then selected. As a similarity metric, cross-lane replay suspicion score Defined as:

[0043] in, This is the minimum Euclidean distance between the net phase difference vector of the current abnormal response and all reference vectors of the adjacent lanes. Score the suspicion of cross-lane replay. The smaller, The closer the value is to 1, the closer the physical signal characteristics of the current abnormal response are to the signal characteristics of a legal passage in an adjacent lane, and the higher the suspicion of cross-lane replay. The above-mentioned abnormal marker includes the tag identifier and timestamp information that triggered the abnormality. After receiving the abnormal marker, the roadside unit of the adjacent vehicle can perform enhanced verification on the subsequent response message with the same tag.

[0044] In this embodiment, during the communication process of the vehicle-mounted electronic tag, steps 3 and 4 perform media compensation based on the vehicle model media parameters to eliminate the additional phase offset introduced by the windshields of different vehicle models, obtaining a net phase difference value reflecting the tag's true spatial location. Step 5 filters and hashes the net phase difference value to generate a phase feature digest value that encodes the unique characteristics of the combination of the tag's physical location and the vehicle model media. Step 6 embeds the phase feature digest value into a block cipher process to generate a desired transition token that integrates physical layer spatial information, making the token verification result dependent on both the temporal offset and the physical layer spatial location information.

[0045] When an attacker replays the intercepted tag response message in an adjacent lane, the phase feature digest value calculated by the roadside unit based on the actual received signal does not match the original phase feature digest value bound to the transition token because the physical location of the replaying device is different from that of the original tag. This causes the token comparison in step 7 to fail. Without the block cipher key, the attacker cannot embed a forged phase feature digest value into the transition token. Therefore, physical layer lane positioning and application layer anti-replay verification are cross-bound through cryptographic operations, preventing attackers from breaking through the two layers of verification separately. This solves the security problem of cross-lane replay attacks succeeding when the two verification methods operate independently and are attacked one by one.

[0046] The following is an example of an application of the present invention, such as Figure 2-9 As shown, the implementation process is as follows: A highway toll station gantry is equipped with 4 roadside antennas. On a certain workday in 20XX, a car (model code: VH-02) was traveling normally in lane 2. Simultaneously, an attacker deployed a replay device in lane 3, attempting to intercept VH-02's response message and replay it in lane 3 to gain free passage. The roadside unit issued an activation command to VH-02, and the session timing reference point is recorded as the moment this activation command was issued.

[0047] Execution process of step 1 The roadside unit sends an activation command to the VH-02 vehicle-mounted electronic tag. The tag extracts the session random number and the current timestamp from the command, records the timestamp as the session timing reference point, and concatenates the session random number with the current value of the tag's internal counter to generate the transition path seed for this session.

[0048] Table 1 Session initialization parameters

[0049] Execution process of step 2 When the tag status transitions from "Active" to "Transaction", calculate the time difference between the current moment and the time series reference point. ms, quantized as millisecond-level time offset. The current state code, target state code, transition path seed, and time offset are input together into the lightweight block cipher unit to generate a transition token.

[0050] Based on time decay function ,in ms, , ms, calculate the attenuation window value The label is sent after embedding the transition token and decay window value into the response message extension field, the counter is incremented to 1025, and the transition path seed is updated synchronously.

[0051] Table 2 Key Fields of Response Message

[0052] Step 3 execution process The roadside unit's four antennas receive the uplink response signal from VH-02, perform carrier synchronization and symbol timing recovery on the raw IQ data of each antenna, and generate four time-aligned synchronous baseband signals. Simultaneously, it parses the vehicle type identifier code VH-02 from the response frame header and retrieves the corresponding windshield parameter group from the local vehicle medium parameter table.

[0053] Table 3. Media Parameters for VH-02 Model

[0054] Step 4 execution process In steps 401 and 402, based on the installation positions of the four antennas on the gantry and the estimated direction of arrival of the tag, the geometric elevation angle between each antenna and the tag is calculated. This allows us to obtain the incident angle of the signal relative to the glass normal. According to Snell's Law Calculate the angle of refraction Then by formula Calculate the additional transmission phase value of each antenna to form a 4-dimensional medium additional phase vector.

[0055] In steps 403 to 405, the conjugate multiplication of the four synchronous baseband signals with adjacent antennas is performed to extract three original phase difference values. Then, the corresponding medium-added phase difference components are subtracted to obtain three net phase difference values.

[0056] Table 4 Phase Calculation Process (Legitimate vehicle VH-02 in lane 2)

[0057] The three original phase difference values, the medium-added phase difference component, and the net phase difference value are shown in the table below.

[0058] Table 5 Calculation results of net phase difference

[0059] Step 5 execution process A sliding window mean filter (window length of 3 frames) is applied to the sequence of three net phase differences to suppress transient jitter caused by multipath and thermal noise, resulting in a stable net phase difference vector. After normalizing each component by fractional scaling, a hash compression operation is performed to generate a fixed-length phase feature digest value.

[0060] Table 6. Phase Feature Summary Generation Process

[0061] Execution process of step 6 The roadside unit extracts the transition token 0xD4B9E2310C7A5F68 and the attenuation window value 27.44ms from the response message. It also extracts the phase feature summary value 0x7E3A9C14 and the roadside unit-side time difference value. The expected value of the local cache counter (1024) and the session random number (0xA3F7C182) are input into the block cipher unit to generate an expected transition token that incorporates physical layer spatial information. Since the phase feature digest value calculated by the roadside unit based on the actual received signal from VH-02 in a legitimate scenario is consistent with the physical environment at the time of tag transmission, the expected transition token is identical to the received transition token.

[0062] Step 7 execution process (legal passage determination) The roadside unit compares the received transition token with the expected transition token bit by bit, and the results match. Simultaneously, verification is performed. Does ms satisfy? ,Right now The timeliness verification passed. Both conditions were met, the response was deemed valid, and the lane 2 ownership result was associated with TAG-VH02-0047 and written into the transaction record.

[0063] Now, we examine a replay attack scenario in lane 3. After intercepting the VH-02's response message, the attacker replays it in lane 3, and the roadside unit receives the replay signal. Because the replay device is located in lane 3, the angle of arrival of the signals received by the four antennas shifts, and the overall geometric elevation angle of each antenna shifts by approximately 8° to 10°. The net phase difference vector after medium compensation becomes... After filtering and hash compression, the phase feature digest value 0x2B51F087 is obtained, which is different from the original value 0x7E3A9C14. In step 6, the roadside unit uses 0x2B51F087 in the cryptographic operation. The generated expected transition token does not match the intercepted original transition token 0xD4B9E2310C7A5F68. The token comparison in step 7 fails, and the response is determined to be abnormal.

[0064] Step 8 execution process After a token matching failure, the roadside unit uses the net phase difference vector of the current abnormal response. For the query vector, calculate the Euclidean distance between it and the net phase difference vector of the valid passage tags recorded within the preset time range for lane 3. Take the minimum Euclidean distance. Substitute into the scoring formula Calculated It exceeds the preset threshold of 0.85.

[0065] Table 7. Suspicion Score for Cross-Lane Replays

[0066] The roadside unit reports the tag identifier, abnormal message characteristics, and phase difference vector deviation information of TAG-VH02-0047 to the background risk control system. At the same time, it broadcasts an abnormal marker containing the tag identifier and timestamp to the roadside units of adjacent lanes, triggering enhanced verification of the subsequent response of the adjacent lane to the tag.

[0067] The entire data flow process embodies the cross-binding logic of the physical layer and the application layer: Steps 1 to 2 embed the timing offset into the transition token on the tag side; Steps 3 to 5 extract the phase feature digest value after medium compensation based on the actual received signal in the roadside unit; Step 6 uses this digest value as the input for cryptographic operations to generate the expected transition token; and the token comparison result in Step 7 therefore depends on both timing information and physical spatial location information. In a replay attack scenario, changes in physical location lead to changes in the phase feature digest value, which in turn causes a mismatch between the expected transition token generated in Step 6 and the intercepted token. Step 8 further quantifies the replay suspicion and triggers risk control linkage, forming a complete protection closed loop from physical layer signal perception to application layer cryptographic verification and then to risk control reporting.

[0068] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. An ETC (Electronic Toll Collection) vehicle-mounted electronic tag and communication method, characterized in that, At least including: The vehicle-mounted electronic tag extracts the session random number and the current timestamp from the activation command of the roadside unit, and concatenates the session random number with the current value of the monotonically increasing counter inside the tag to generate a transition path seed; When a state transition is triggered, the state code, the transition path seed, and the timing offset are input into the block cipher arithmetic unit to generate a transition token. The transition token and the attenuation window value are then embedded into the response message and sent to the roadside unit. The roadside unit performs baseband processing on the response signals received by multiple antennas to obtain a synchronous baseband signal, and performs medium compensation on the phase difference between adjacent antennas in combination with vehicle model medium parameters to obtain a net phase difference value. The net phase difference value is then hash-compressed to generate a phase feature summary value. The phase feature digest value and the session timing parameters are input into the block cipher arithmetic unit to generate the expected transition token. The received transition token is compared with the expected transition token, and the time difference is verified to see if it is within the effective range of the decay window, thereby determining the legality of the transaction.

2. The ETC on-board electronic tag and communication method according to claim 1, characterized in that, The decay window value is generated based on the state transition timing decay function, which takes the timing offset as the independent variable and outputs a decay window value that decreases monotonically with the timing offset. The time offset is the time difference between the current time and the time reference point determined by the current timestamp, which is obtained by quantization with a preset precision.

3. The ETC on-board electronic tag and communication method according to claim 1, characterized in that, The process of obtaining a net phase difference value by compensating for the phase difference between adjacent antennas based on vehicle model medium parameters includes: Parse the vehicle type identification code from the response frame header, and retrieve the windshield nominal tilt angle, glass thickness and dielectric constant parameter group from the vehicle medium parameter table based on the vehicle type identification code; Based on the geometric installation position of the gantry antenna array and the estimated direction of arrival of the tag, calculate the geometric elevation angle between each antenna and the tag; For each antenna, the corresponding geometric elevation angle is taken as the incident angle, and the nominal tilt angle, glass thickness and dielectric constant parameter set are taken as the medium parameters. The plane wave oblique incidence multilayer medium transmission model is input to calculate the additional transmission phase value when the signal penetrates the windshield and generate the medium additional phase vector. The original phase difference value is extracted by performing conjugate multiplication on adjacent antennas in the synchronous baseband signal. The corresponding medium-added phase difference component is then subtracted from each original phase difference value to obtain the medium-compensated net phase difference value.

4. The ETC on-board electronic tag and communication method according to claim 3, characterized in that, The plane wave oblique incidence multilayer dielectric transmission model treats the windshield as a planar dielectric layer with a uniform dielectric constant, and for the first... For an antenna, the incident angle of the signal relative to the glass normal is determined based on the geometric elevation angle and the nominal tilt angle. Then, the refraction angle of the signal inside the glass is calculated based on Snell's law. Based on the refraction angle and the glass thickness, the propagation path length of the signal along the refraction direction within the glass layer is determined. The additional transmission phase value corresponding to the antenna is calculated by combining the free space wavenumber and the square root of the dielectric constant.

5. The ETC on-board electronic tag and communication method according to claim 3, characterized in that, The step of subtracting the corresponding medium-added phase difference component from each original phase difference value includes: The first Subtract the first phase difference in the dielectric-added phase vector from the original phase difference between adjacent antennas. The component and the first The difference of the nth component is used to obtain the nth component. The net phase difference after media compensation, among which The range of values ​​is to , This represents the total number of roadside antennas.

6. The ETC on-board electronic tag and communication method according to claim 1, characterized in that, The step of performing hash compression on the net phase difference to generate a phase feature digest value includes: A stable net phase difference vector is obtained by applying a sliding window mean filter to the sequence of net phase difference values. After performing fractional scaling normalization on each component of the stable net phase difference vector, a hash compression operation is performed to generate a fixed-length phase feature summary value.

7. The ETC on-board electronic tag and communication method according to claim 1, characterized in that, The determination of the legality of the transaction based on this includes: If the tokens match and the time difference is within the effective range of the decay window, the response is deemed valid. The lane ownership result determined based on the stable net phase difference vector is then bound to the vehicle electronic tag identity information, and the transaction is advanced to the next state. If token matching fails or the time difference exceeds the decay window, the response is considered abnormal.

8. The ETC on-board electronic tag and communication method according to claim 7, characterized in that, When determining an abnormal response, the following is also included: The vector distance between the net phase difference vector of the current abnormal response and the net phase difference vector of the historical passage tag of the adjacent lane is calculated to generate a cross-lane replay suspicion score. If the cross-lane replay suspicion score exceeds the preset threshold, the corresponding tag, abnormal message characteristics and phase difference vector deviation information will be reported to the background risk control system, and the abnormal marker will be broadcast to the adjacent vehicle roadside unit.

9. The ETC on-board electronic tag and communication method according to claim 8, characterized in that, The vector distance calculation uses the Euclidean distance algorithm, with the net phase difference vector of the current abnormal response as the query vector, and the net phase difference vector of each legal passage tag recorded by the adjacent lane within a preset time range as the reference vector, and the minimum value among all Euclidean distances is taken as the similarity measure. The cross-lane replay suspicion score is the reciprocal of the sum of the minimum value and a constant. The smaller the minimum value, the higher the cross-lane replay suspicion score.

10. An ETC (Electronic Toll Collection) vehicle-mounted electronic tag and communication system, used to execute the ETC vehicle-mounted electronic tag and communication method according to any one of claims 1 to 9, characterized in that, include: The session parameter extraction and seed generation module is used to extract the session random number and the current timestamp from the activation command of the roadside unit, and to concatenate the session random number with the current value of the monotonically increasing counter inside the tag to generate the jump path seed. The token generation and response sending module is used to input the state code, the transition path seed and the timing offset into the block cipher operation unit to generate a transition token when the state transition is triggered, and to embed the transition token and the attenuation window value into the response message and send it to the roadside unit. The signal processing and medium compensation module is used to perform baseband processing on the response signals received by multiple antennas to obtain a synchronous baseband signal, and to perform medium compensation on the phase difference between adjacent antennas in combination with the vehicle model medium parameters to obtain a net phase difference value. A phase feature summary generation module is used to perform hash compression on the net phase difference to generate a phase feature summary value; The expected token generation module is used to input the phase feature digest value and the session timing parameters into the block cipher arithmetic unit to generate the expected transition token. The transaction validity determination module is used to compare the received transition token with the expected transition token and verify whether the time difference is within the effective range of the decay window, thereby determining the validity of the transaction.

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